Tape cassette having tapered guide pins press-fitted into cassette wall and grease lubricant for rollers

ABSTRACT

A tape cassette comprises a supply and a take-up reel on which tape is wound, a cassette casing for rotatably enclosing the reels therein, a plurality of tape guide pins, each being press-fitted through the inner wall of the casing, for defining a tape path for the tape travelling between the pair of reels. The press-fit section of each guide pin is formed in a predetermined taper in such a manner as to gradually decrease its outer diameter towards its end. The straight press-fit section of the guide pin is formed in such a manner as to include a predetermined geometry of chamfered circumference at its end. In a tape guide pin used in conjunction with a tape guide roller, grease having a predetermined viscosity coefficient is disposed between the associated pin and roller. An electrical insulating cover is provided for surrounding the exposed underside of the electrically conductive lower half of the casing.

This is a continuation of application Ser. No. 448,622, filed 12-11-89,now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tape cassette which is optimallyadapted for use in recording and/or reproducing apparatus. Specificallyto a tape cassette wherein tape guide pins are press-fitted onto acassette casing.

2. Description of the Prior Disclosure

Recently, there have been proposed and developed various magnetic tapecassettes to serve as an external data storage medium.

One such magnetic tape cassette has been disclosed in U.S. Pat. No.4,198,013. This conventional tape cassette includes a pair of reels,namely a supply reel and a take-up reel, rotatably supported in thecassette casing. As is generally known, magnetic tape is wound on thepair of reels through a plurality of tape guide pins by which thetravelling path of the tape is controlled in such a manner that the tapeis wound on the reels at a predetermined contact angle. That is, thetape travelling path is defined by the upstanding guide pins, eacharranged at a predetermined location on the cassette casing. As shown inFIG. 1, a conventional guide pin 90 is integrally formed with a tapecontact section 90a, upper and lower flange sections 90b, and apress-fit section 90c extending from the bottom surface of the lowerflange section. Each section 90a, 90b, or 90c has a specific, constantouter diameter. As seen in FIG. 1, the guide pin 90 is fixed on thecassette casing such that the press-fit section 90c is press-fitted ontothe aluminum alloy lower half of the casing. Such guide pins aretraditionally formed by lathe machining. The machining accuracy may beaffected by various machining conditions, such as deflection of theworkpiece, fluctuation in bite by a cutting tool, and fluctuation inlubrication by a cutting lubricant. For example, as shown in FIG. 2, thepress-fit section 90c is often formed in a reverse taper fashion inwhich the outer diameter is gradually increased from its root connectedto the bottom surface of the lower flange section 90b to its end.Therefore, the outer diameter a at the root is slightly smaller thanthat b at the end. If such a reverse tapered press-fit section of theguide pin is press-fitted into the lower half of the casing, thegreatest outer diameter of end of the press-fit section 90c expands apreformed hole and forms a hole 33 slightly greater than a requiredouter diameter of hole, over the whole length of press-fit section 90c.As a result, after pressing, pressure occurring between the outerperiphery of the press-fit section 90c and the inner periphery of thehole formed in the lower half of the cassette casing is decreased. Underthese conditions, since the guide pin 90 is not press-fitted tightlyenough into the lower half, the guide pin 90 may be easily removed fromthe lower half. Therefore, there is a possibility that the guide pinsmay dislodge due to external forces, such as vibration.

During press-fitting of a guide pin, a maximum impact with regard to thelower half occurs at the beginning of pressing. Specifically, since theend of the reverse tapered press-fit section 90c has a maximum outerdiameter, the initial impact during pressing becomes excessively high,thereby resulting in deformation or damage to the lower half. Therefore,the flatness of the lower half may be compromised and as a result tapetravel may become unstable. The above mentioned defect of areverse-tapered press-fit section for a guide pin may also occur to somedegree in a non-tapered, or straight press-fit section for a guide pin.If a reverse-tapered or straight press-fit section is press-fitted ontothe lower half of a cassette without any preformed hole, the flatness ofthe lower half may be compromised to a greater degree, due to theexcessively high, initial impact necessary during pressing and inaddition such guide pins may also be dislodged relatively easily byexternal forces. Traditionally, such a guide pin is used in the lowerhalf of a casing in such a manner as to directly guide magnetic tape onits cylindrical outer peripheral surface or to guide magnetic tape via aguide roller rotatably assembled therearound. In general, since thesurfaces of such conventional guide pins are finished within a range ofa maximum surface-roughness Rmax 0.5 to 0.8 μm, there is a possibilitythat dust may be generated at the point of contact between the guidepins and the coated tape surface, resulting in so-called dropout errorif the tape cassette is used for a relatively long time. In a guide pinemploying the guide roller, since magnetic tape is guided by the outerperipheral surface of the guide roller, generation of the previouslydescribed dust is reduced. Such guide rollers may provide extremelysmooth tape feed, however this makes tape tension control quitedifficult.

Furthermore, in tape cassettes including such press-fitted guide pins,the lower half, receiving the guide pins, is made of electricallyconductive material, such as aluminum alloy, as previously described.Therefore, were an user, charged with static electricity to touch thelower half of the casing of the tape cassette while loading therecording and/or reproducing apparatus for operation, static electricitymay be discharged through the lower half of the cassette, through thecassette holder of the apparatus into the electrical control unitincluding logical circuits, resulting in error of logical circuitsbecause of their low degree of tolerance to static electricity.

SUMMARY OF THE INVENTION

It is, therefore in view of the above disadvantages, an object of thepresent invention to provide a tape cassette in which a tape guide pinis firmly press-fitted into a cassette casing.

It is another object of the invention to provide a tape cassette whichis capable of maintaining a high degree of flatness in the casing evenafter guide pins have been press-fitted to the casing.

It is a further object of the invention to provide a tape cassette whichcan provide optimal tape tension during tape travel.

It is another object of the invention to provide a tape cassette whichis capable of preventing static electricity from a user from beingintroduced through the cassette casing to electric or electronicelements in the associated recording and/or reproducing apparatus.

It is a still further object of the invention to provide a tape cassettewhich has high durability and high reliability to maintain high qualityas a recording medium.

In order to accomplish the aforementioned and other objects, a tapecassette comprises a pair of reels mounted side by side, on which tapeis wound, a cassette casing for rotatably enclosing the pair of reelstherein, at least one tape guide pin being press-fitted through the wallof the casing, for defining a tape path for tape travel between the pairof reels. The guide pin include a press-fit section press-fitted intothe casing. The press-fit section is formed in a taper fashion in such amanner as to gradually decrease its outer diameter towards the end ofthe press-fit section. Preferably, the press-fit section may befrusto-conical, and its taper may be within a range of 1/250 to 1/38 toinsure optimum press-fit with the casing.

According to another aspect of the invention, a tape cassette comprisesa pair of reels mounted side by side, on which tape is wound, a cassettecasing for rotatably enclosing the pair of reels therein, an upstandingpin being press-fitted through the wall of the casing. The pin includesa cylindrical press-fit section to be press-fitted into the casingwithout need of a preformed hole. The press-fit section includes acylindrical outer peripheral surface coaxial to the axis of the pin, achamfered annular circumference at the lower tip of the cylindricalsurface, terminating in a flat circular end perpendicular to the axisand having an outer diameter less than that of the cylindrical surface.The chamfered annular circumference is formed with a curved surface, thecurve, in cross-section, corresponding to the perimeter of a circle witha radius in a range of 0.2 to 0.3 mm, or with a 45° sloped,frusto-conical surface essentially corresponding to the dimension of thecurved surface.

The tape guide pin or upstanding pin may be formed of non-magneticstainless steel material by lathe machining. When the tapered orchamfered pin is used in a manner so as to contact with a tape surfacehaving magnetic substance, its contacting surface has a maximum surfaceroughness of Rmax 0.1 to 0.4 μm to provide smooth tape travel. Thecontacting surface is finished by super-finishing after centerlessgrinding so as to accomplish a maximum surface-roughness of Rmax 0.1 to0.4 μm.

The casing is comprised of an upper half formed of electrical insulatingmaterial and a lower half formed of electrically conductive metalmaterial suitable for the press-fitting of the tape guide pin or theupstanding pin. When a portion of the conductive lower half is exposedoutside of a recording and/or reproducing apparatus in a state whereinthe tape cassette is set to a predetermined loaded position, the casingmay preferably include an insulating member for electrically insulatingthe conductive half, for preventing static electricity from beingintroduced through an exposed portion of the conductive half into theapparatus. The insulating member comprises the outer wall of the casingsurrounding the outer perimeter of the conductive half. The insulatingmember overlaps the exposed underside of the conductive half bysubstantially 20 mm.

According to a further aspect of the invention, a tape cassettecomprises a pair of reels mounted side by side, on which tape is wound,a cassette casing for rotatably enclosing the pair of reels therein, adriven roller being rotated by a drive device of a recording and/orreproducing apparatus, associated with the tape cassette, the drivenroller rotatably supported by an upstanding roller shaft fixed on thewall of the casing, a pair of idle rollers, each rotatably supported byan upstanding roller shaft fixed on the wall of the casing, an endlessflexible drive belt for drivingly engaging the driven roller and theidle rollers to rotate the reels, such that a portion of the drive beltbetween the driven roller and each idle roller pressingly contacts aportion of the outermost peripheral surface of the tape wound on eachreel, the drive belt being driven according to rotation of the drivenroller, and means for controlling tape tension of the tape duringoperation of the tape cassette, the means including grease disposedbetween the associated rollers and shafts for lubricating the contactingsurfaces therebetween, with a predetermined viscous drag. The greaseincludes a viscosity coefficient of 50 to 500 P (poise) within a greasetemperature range of -10° to 60° C. Each of the roller shafts may bepress-fitted through the wall of the casing. The roller shaft includes apress-fit section formed in taper fashion such as to gradually decreaseits outer diameter towards its end. Preferably, the press-fit section isfrusto-conical, and its taper is within a range of 1/250 to 1/38. Theroller shaft may also include a cylindrical press-fit sectionpress-fitted into the casing without a preformed hole. The press-fitsection includes a cylindrical outer peripheral surface coaxial to theaxis of the pin, a chamfered annular circumference at the lower tip ofthe cylindrical surface, terminating in a flat circular endperpendicular to the axis and having an outer diameter less than that ofthe cylindrical surface. The chamfered annular circumference is formedwith a curved surface, the curve, in cross-section, corresponding to theperimeter of a circle with a radius in a range of 0.2 to 0.3 mm, or witha 45° sloped, frusto-conical surface essentially corresponding to thedimension of the curved surface.

According to a still further aspect of the invention, a tape cassettecomprises a pair of reels mounted side by side, on which tape is wound,a cassette casing for rotatably enclosing the pair of reels therein, thecasing partially including an electrically conductive sectionconstructed such that a portion of the conductive section is exposedoutside of a recording and/or reproducing apparatus in a state whereinthe tape cassette is set to a predetermined loaded position, aninsulating member for electrically insulating the conductive section,for preventing static electricity from being introduced through anexposed portion of the conductive section into the apparatus. Theinsulating member comprises the outer wall of the casing surrounding theouter perimeter of the conductive section. The casing is comprised of apair of halves. The insulating member overlaps the underside of theconductive section by mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section view illustrating a tape guide pin used forconventional magnetic tape cassettes at a state wherein the guide pin ispress-fitted into the lower half cassette casing.

FIG. 2 is a partial front illustrating a guide pin of the conventionalmagnetic tape cassette including a reverse tapered press-fit section.

FIG. 3A is a sectional view illustrating a flanged tape guide pin of atape cassette according to the invention at a state just before theflanged guide pin is press-fitted into the lower half of the cassettecasing.

FIG. 3B is a sectional view illustrating the flanged guide pin as shownin FIG. 3A at a state wherein the guide pin is press-fitted into lowerhalf of the cassette casing.

FIG. 4A is a sectional view illustrating a straight guide pin of a tapecassette according to the invention at a state just before the straightguide pin without a flange section is press-fitted into the lower halfof the cassette casing.

FIG. 4B is a sectional view illustrating the straight guide pin as shownin FIG. 4A at a state wherein the straight guide pin is press-fittedinto the lower half of the cassette casing.

FIG. 5 is an exploded perspective view illustrating a tape cassetteaccording to the invention.

FIG. 6 is a plan view illustrating a tape cassette according to theinvention under a condition wherein the upper half has been removed.

FIGS. 7A to 7D are partial cross sectional views illustrating a pressingprocess for a straight press-fit section of the guide pin according tothe invention including a predetermined geometry of chamferedcircumference at the base of the pin.

FIG. 8 is a partial cross sectional view illustrating thecross-sectional configuration of the hole punched by the straightpress-fit section of the guide pin according to the invention.

FIG. 9 is a cross sectional view taken along line IX--IX of FIG. 6.

FIG. 10 is a graph illustrating the tape tension relationship relativeto the viscosity coefficient of grease disposed between the associatedtape guide roller and the shaft.

FIG. 11 is a partial sectional view illustrating the tape cassetteaccording to the invention in a state wherein the cassette is insertedat a predetermined loaded position in a recording and/or reproducingapparatus.

FIG. 12 is a perspective view illustrating the bottom surface of thelower half of the casing showing the attachment of an electricallyinsulating frame.

FIG. 13 is a graph illustrating the degree of tracking error with regardto the number of completed (full-length) tape travels when comparing theconventional tape cassette C and the improved tape cassette I accordingto the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The principles of the present invention, applied to a tape cassette forrecording and/or reproducing apparatus, are illustrated in FIGS. 3A to13.

Referring now to FIGS. 5 and 6, a tape cassette according to theinvention includes an upper half 2 formed of electrical insulatingsynthetic resin and a flat, lower half 3 formed of aluminum alloytogether forming a cassette casing 1. The upper half 2 is comprised of asubstantially flat, upper wall and a side wall 4 extending downward fromthe outer perimeter of the upper wall. The casing 1 defines an internalspace for rotatably supporting a pair of reels, one being a supply reel5 and the other a take-up reel 6, in such a manner that the edge of sidewall 4 abuts the outer perimeter of the lower half 3. Magnetic tape 7 iswound on the pair of reels 5 and 6 through a plurality of upstandingtape guide pins which are firmly disposed on the lower half 3. The pathof tape travel is defined by the guide pins, each arranged at apredetermined location on the lower half 3 of the casing 1. As best seenin FIG. 6, two flanged guide pins 9 and 10, are located near the frontface of the casing 1, and straight guide pins 11, 12, and 13, arerespectively located between the supply reel 5 and the guide pin 9,between the two guide pins 9 and 10, and between the guide pin 10 andthe take-up reel 6. Tape from the supply reel 5 is drawn over the guidepin 9 at a predetermined contact angle, thus changing the direction oftape travel. Thereafter, the tape travels parallel to and in thevicinity of the front face of the casing 1. Subsequently, the tape isdrawn over the guide pin 10 at a predetermined contact angle and againthe tape travelling direction is changed to facilitate the tape beingwound finally on the take-up reel 6.

As clearly seen in FIGS. 3A and 3B, the flanged guide pins 9, 10 areintegrally formed with tape contact sections 9a, 10a, upper and lowerflange sections 9b, 10b, and frusto-conical press-fit sections 9c, 10c,respectively. These guide pins 9 and 10 are formed of non-magneticstainless steel material by lathe machining. As previously described,the tape contact sections 9a, 10a permit tape to be wound thereon at thepredetermined contact angle. The upper and lower flange sections 9b,10b, restrict lateral movement of the tape 7. The press-fit sections 9c,10c are formed in a taper fashion wherein the outer diameter isgradually decreased from the root, connected to the bottom surface ofthe lower flange section 9b, to the end. Assuming that dimensions A, B,are taken as shown in FIG. 3A, it is desirable that the taper (A-B)/ ofthe press-fit section 9c, 10c be selected within a range between 1/250to 1/38. If the taper dimensions exceed the above mentioned desirabletaper, it is difficult to insure that high flatness of the lower half 3is reliably maintained due to the high stress that would be generated inpressing the guide pins to the lower half 3. Conversely, if the taperdimensions are less than the desirable taper, there is a possibilitythat the press-fit section of the guide pin will become straight, or areverse taper may be formed which would be unsuited to press-fitting,due to fluctuations in lathe machining accuracy.

As clearly seen in FIGS. 4A and 4B, the straight guide pins 11, 12, and13 are integrally formed with tape contact sections 11a, 12a, and 13a,and frusto-conical press-fit sections 11b, 12b, and 13b, respectively.The guide pins 11, 12, and 13 are formed of non-magnetic stainless steelmaterial by lathe machining. The press-fit sections 11b, 12b, and 13bare formed within the same taper range as the press-fit sections 9c,10c. As seen in FIG. 6, out of the three straight guide pins 11, 12, and13, only guide pins 11 and 13 come into contact with the oxide(recording) surface of the tape, while the guide pin 12 comes intocontact only with the uncoated surface of the tape. In this embodiment,the maximum surface-roughness Rmax 0.1 to 0.4 μm of the pins 11 and 13is less than the maximum surface-roughness Rmax 0.5 to 0.8 μm ofconventional guide pins, thereby reducing dust generated at the point ofcontact between the guide pins and the coated tape surface. In thismanner, so-called dropout error, due to abrasion of the magnetic oxideat a certain point on the tape, is prevented. The magnetic tape cassetteaccording to the embodiment has high durability and high reliability asa high quality recording medium. Desirably, the outer peripheralsurfaces of the guide pins 11 and 13 are finished by super-finishingafter centerless grinding, so as to accomplish a maximumsurface-roughness of Rmax 0.1 to 0.4 μm with regard thereto. If thesurface-roughness Rmax is less than 0.1 μm, there is a tendency for thetape surface and the outer peripheral surfaces of the guide pins 11 and13 to adhere to each other. Therefore, as set forth, it is desirablethat the surface-roughness Rmax of the outer peripheral surface of thetwo pins 11 and 13 be selected within a range of 0.1 to 0.4 μm. Inconstructions according to the embodiment, the flanged guide pins 9 and10 are aligned with holes 32 formed in the lower half 3 as shown in FIG.3A and thus the guide pins 9 and 10 are press-fitted onto the lower half3 as shown in FIG. 3B. While as shown in FIG. 4A, the straight guidepins 11 to 13 are directly pressed into the lower half 3 withoutpreformed holes and thus the guide pins 11 to 13 are press-fitted ontothe lower half 3 as shown in FIG. 4B. As shown in FIG. 4A, note that thecircular end surface of each press-fit section of the straight guidepins 11, 12, and 13 is flat and perpendicular to the axis of the guidepin so as to provide an optimal pressing. In the above mentionedpressing method, the necessity of having preformed holes with regard tothe lower half is determined depending on the outer diameter of thepress-fit section of the guide pin in conjunction with the mechanicalstrength of the lower half of the casing.

In the pressing process, since the press-fit sections 9a to 13a areformed in a taper fashion, pressing is accomplished in such a mannerthat the hole is gradually expanded over the entire surface of thepress-fit section according to the press-fitting stroke, so that afterthe pressing is completed, pressure occurring between the press-fitsection and the lower half exceeds a required pressure over the wholesurface of the press-fit section. When these conditions are met, theguide pins 9 to 13 are firmly connected to the lower half 3, such thatthese guide pins cannot be easily removed. In such tapered guide pins,since the end of the press-fit section has the smallest diameter, theinitial impact occurring at the beginning of the pressing stroke issuppressed to a minimum value, thereby providing smooth pressing. Thisprevents the lower half 3 from deforming due to excessive initial impactduring pressing. As a result, high flatness of the lower half 3 may bemaintained.

As shown in FIGS. 7A to 7D, the previously described straight guide pins11 to 13, each including a tapered press-fit section and directlypress-fitted into the lower half without preformed holes, may bereplaced with a guide pin 28 including a chamfered press-fit section 29which has a chamfered annular circumference 29c at the end. The guidepin 28 will be referred to as a "hamfered guide pin". The pressingprocess is started from the starting state of FIG. 7A, and continues viathe intermediate pressing states of FIGS. 7B and 7C, to the pressingcompleted state of FIG. 7D, in that order. In FIGS. 7A to 7D, thepress-fit section 29 corresponds to the section lower than the phantomline. As clearly seen in FIG. 7A, the chamfered press-fit section 29includes a cylindrical outer peripheral surface 29b of an outer diameterD₂ and a circular, flat end surface 29a of an outer diameter D₁ lessthan the diameter D₂. The press-fit section 29 also includes thechamfered annular circumference 29c joining the flat end surface 29a andthe outer peripheral surface 29b. Preferably, the chamferedcircumference 29c may be formed with a surface curved (in cross-section)within the range of a radius R of 0.2 to 0.3 mm or with a 45° sloped,frusto-conical surface essentially equivalent to the above mentionedcurved surface.

The pressing process of FIGS. 7A to 7D is achieved according to thefollowing steps.

First, as shown in FIG. 7A, the press-fit section 29 is presseddownwardly to the upper press-fit surface of the lower half 3 in a statewherein the flat end surface 29a and the press-fitted surface areparallel with each other and the axis of the guide pin is arrangedperpendicularly to the upper surface of the lower half 3.

As shown in FIG. 7B, the end surface 29a reaches and pressingly abutsthe upper surface of the lower half 3. Thereafter, shearing fractureindicated by reference numeral s of FIG. 7B occurs at an essentiallycylindrical portion of the lower half 3 along the outermostcircumference (diameter D₁) of the end surface 29a. According tosubsequent pressing, the shearing fracture grows gradually towards thelower surface of the lower half 3. As seen in FIG. 7C, a hole 34 formedby the shearing fracture includes a substantially cylindrical shearedsurface and a substantially frusto-conical broken-out surface extendingor growing gradually from the sheared surface to the lower surface ofthe lower half 3. Assuming that the length of the press-fit section 29is set to a length of 2T/3 with regard to a thickness T of the lowerhalf 3, the sheared surface and the broken-out surface respectivelycorrespond to a length 2T/3 and a length T/3, as shown in FIG. 7C. Inother words, the shearing fructure reaches the 2T/3 length of the lowerhalf 3 and thereafter the lower section of the lower half correspondingto the T/3 length is broken out. In this manner, while a portion of thelower half is punched out as a punched portion 35, the press-fit section29 is gradually press-fitted into the hole 34 in such a manner as toexpand the inner diameter of the hole 34 by means of the chamfered lowercircumference 29c. Thus, the pressing is completed as seen in FIG. 7D.If the guide pin 28 is forcibly removed from the lower half 3 aftercompletion of the pressing as shown in FIG. 7D, the inner diameter ofthe hole 34 may become substantially equal to the outer diameter D₁ ofthe outermost circumference of the end surface 29a as shown in FIG. 8.That is, after completion of pressing, the hole 34 is expanded by thedifference between the inner diameter of the hole 34 (substantiallyequal to the diameter D₁) and the outer diameter D₂ of the cylindricalouter periphery of the press-fit section 29. In other words, accordingto the above pressing method, pressure generated due to elasticdeformation of the inner periphery of the hole 34 corresponding to theabove mentioned difference is to the outer peripheral surface 29b of thepress-fit section 29.

In conventional straight guide pins, the curved surface of the chamferedcircumference of the press-fit section is formed at a relatively smallradius, such as 0.1 mm, according to research by the inventors of thisinvention. When comparing the radii R of 0.1 mm and 0.2 to 0.3 mm, theforce F required to remove the guide pin 28 from a lower half 3 having athickness T of 2 mm is indicated, according to the outer diameter D₂ ofthe press-fit section 29 of the guide pin 28, in the Table 1. This datawas experimentally confirmed by the inventors.

                  TABLE 1                                                         ______________________________________                                        Thickness T                                                                              Diameter D.sub.2                                                                            Radius R Force F                                     (mm)       (mm)          (mm)     (kg)                                        ______________________________________                                                                 0.2-0.3  80                                          2          2.3           0.1      70                                                                   0.2-0.3  90                                          2          3.4           0.1      70                                                                   0.2-0.3  130                                         2          3.9           0.1      90                                          ______________________________________                                    

As will be appreciated from Table 1, a chamfered guide pin 28 having acurved surface along a radius R of 0.2 to 0.3 mm according to theinvention is inferior to conventional guide pins having a curved surfacealong a radius R of 0.1 mm, with regard to the removing force F. If theradius R exceeds 0.3 mm, the hole 34 is excessively, elasticallydeformed and, as a result, high flatness of the lower half 3 may not bemaintained.

Although the previously described pins, including tapered or chamferedpress-fit sections, serve as tape guide pins or tape guide rollershafts, these pins may also serve as a pivot shaft, a supporting shaftor the like.

The tape cassette casing 1 also includes a tape exposure section 20through which some of the tape 7 is exposed to the outside of thecasing 1. The tape exposure section 20 is provided within the straighttape travel path between the flanged guide pins 9 and 10, such that thecoated tape surface and a recording and/or reproducing head may comeinto contact with each other during recording and/or reproducing. Thecut-out portion 21 of the tape exposure section 20 is hermeticallycovered by a pivotable cover 23 to prevent dust from entering thecasing 1. The cover 23 is pivotably supported by an upstanding pin 30provided on the lower half 3. The cover 23 is normally biased in aclosed position by means of a coil spring 31. During recording and/orreproducing, the cover 23 is opened by a releasing device (not shown)provided in the recording and/or reproducing apparatus (not shown).

A tape travelling mechanism 14 includes a driven roller 15, disposedsubstantially midway between the two flanged guide pins 9 and 10, andtwo idle rollers 16 and 17, disposed in the vicinity of both corners ofthe rear surface of the casing 1. These rollers 15, 16, and 17 arerotatably supported by means of upstanding roller shafts 18 provided onthe lower half 3. The driven roller 15 is comprised of a drive beltcontact section, on which a flexible drive belt 25 is wound, and a driveroller abutting section 15a, which has an outer diameter greater thanthe drive belt contact section and is driven by a drive roller (notshown) of a tape drive device (not shown) provided in the recordingand/or reproducing apparatus, during recording and/or reproducing. Forthis reason, a portion of the drive roller abutting section 15a isexposed through an opening 19 formed substantially in the center of thefront face of the casing 1. As best seen in FIG. 6, the flexible drivebelt 25 is endless and is wound in a manner so as to engage the abovementioned rollers 15, 16, and 17. Since the endless belt 25 is flexible,a portion of the drive belt between the driven roller 15 and the idleroller 17 pressingly contacts a portion of the outermost peripheralsurface of magnetic tape 7 wound on the supply reel 5, while a portionof the drive belt between the driven roller 15 and the idle roller 16,pressingly contacts a portion of the outermost peripheral surface ofmagnetic tape 7 wound on the take-up reel 6 to turn the reels 5 and 6when the belt 25 is driven via the driven roller 15.

As shown in FIG. 9, contacting surfaces between the respectiveassociated rollers 15, 16, and 17 and shafts 18 are greased to preventabrasion. According to the invention, grease 24 includes a viscositycoefficient of 50 to 500 poise within a range of grease temperature from-10° to 60° C. In this embodiment, a maximum surface roughness Rmax ofthe inner peripheral surface of the roller is designed to a value lessthan 0.1 μm and a maximum surface roughness Rmax of the outer peripheralsurface of the shaft 18 is designed within a range of 0.2 to 0.6 μm. InFIG. 8, reference numeral 22 denotes a snap ring provided to restrictmovement of the roller 16 in the axial direction of the shaft 18.

The magnetic tape cassette according to the invention operates asfollows.

When the tape cassette is inserted into a loading holder (not shown)provided in the recording and/or reproducing apparatus and tape loadingis started, the cover 23 is rotated to an open position against thespring force generated by the spring 31. Upon sufficient opening of thecover 23, the recording and/or reproducing head (not shown) of therecording and/or reproducing apparatus is pressed against the magnetictape exposed through the tape exposure section 20 and simultaneously thedrive roller (not shown) of the tape drive device (not shown) is pressedon the abutting section 15a of the driven roller 15. According torotation of the drive roller of the tape drive device, the driven roller15 is rotated and as a result the idle rollers 16 and 17 are driven bymeans of the drive belt 25. As shown in FIG. 6, assuming the drive belt25 is driven in one direction indicated by the three arrows g, themagnetic tape 7 will be driven in the opposite direction indicated bytwo arrows h by frictional force created at the contacting portionsbetween the magnetic tape 7 and the endless drive belt 25. In thismanner, tape recording and/or reproducing may be executed.

When the drive belt 25 is driven according to rotation of the driveroller of the tape drive device, each idle roller (16,17) is rotatedagainst the viscous drag of grease 24 disposed between the innerperipheral surface of the roller and the outer peripheral surface of theshaft. As best seen in FIG. 6, assuming the drive belt 25 is driven inthe direction indicated by the arrows g, the tension of the drive beltbetween the driven roller 15 and the idle roller 16 is slightlydecreased by viscous drag of grease disposed between the idle roller 16and the shaft 18 and while the tension of the drive belt between thedriven roller 15 and the idle roller 17 is slightly increased by viscousdrag of grease disposed between the idle roller 17 and the shaft 18.Conversely, when the drive belt 25 is driven in the opposite direction,the belt tension between the driven roller 15 and the idle roller 16 isslightly increased and the belt tension between the driven roller 15 andthe idle roller 17 is slightly decreased, for the same reasons describedabove. In this manner, the viscous drag of the grease results in belttension adjustment between a belt section tightened between the tworollers (15, 16) via the outer periphery of the magnetic tape wound onthe reel 6, and a belt section tightened between the two rollers (15,17) via the outer periphery of the magnetic tape wound on the reel 5. Asset forth above, since the magnetic tape 7 is driven by frictional forcecreated at the contacting portions between the magnetic tape 7 and thedrive belt 25, assuming that the drive belt 25 is driven in onedirection indicated by the arrows g, the slightly increased belt tensionis applied to the outer periphery of the magnetic tape wound on the reel5 serving as a take-up reel and the slightly decreased belt tension isapplied to the outer periphery of the magnetic tape wound on the reel 6serving as a supply reel. In other words, the tape tension differencebetween the take-up and supply reels is proportional to the belt tensiondifference. In this way, the tape tension is optimally adjusted by theviscous drag of grease 24 having a predetermined viscosity coefficient,such that the tension of the take-up reel side becomes slightly higherthan the supply reel side. As shown in FIG. 10, it has beenexperimentally proven by the inventors that the tape tension is stablewithin an optimal tape tension range of 30 to 90 g when the viscositycoefficient of grease 24 is within a range of 50 to 500 P (poise).

In magnetic tape cassettes employing tape guide pins press-fitted intothe lower half of the casing, since the lower half 3 of the cassettecasing 1 is conventionally made of an electrically conductive material,such as aluminium alloy, if the tape cassette is set in the cassetteholder of the recording and/or reproducing apparatus 100 as shown inFIG. 11, such that a portion of the cassette casing 1 is exposed outsideof the apparatus 100, there is the possibility that a user may touch theexposed portion of the tape cassette. As previously described, duringoperation of the apparatus 100 there is a tendency for staticelectricity from the user to be discharged through the exposed portionof the electrically conductive lower half into the electrical controlunit of the apparatus. To prevent this, an electrically insulating coveror frame 24 is attached to the lower half 3 in such a manner as toborder the outer perimeter of the bottom surface of the lower half 3 ata 30 width of substantially 20 mm, as clearly seen in FIG. 12. Withthese constructions, the magnetic tape cassette according to theinvention, has high durability and high reliability to maintain highquality as a recording medium.

As shown in FIG. 13, when comparing a conventional magnetic tapecassette C and a magnetic tape cassette I of the present embodiment, thetape cassette I ameliorates the degree of tracking error or readingerror relative to the number of completed tape travels.

As will be appreciated from the above, although in the presentembodiments according to the invention, a tape cassette includingmagnetic tape is used as a recording medium, another type tape cassettemay be used as such a recording medium.

While the foregoing is a description of the preferred embodiments forcarrying out the invention, it will be understood that the invention isnot limited to the particular embodiments shown and described herein,but may include variations and modifications without departing from thescope or spirit of this invention as described by the following claims.

What is claimed is:
 1. A tape cassette comprising:a pair of reelsmounted side by side, on which magnetic tape is wound; a cassette casingfor rotatably enclosing said pair of reels therein; at least one tapeguide pin being press-fitted through the wall of said casing, fordefining a tape path for tape travel between the pair of reels; and saidguide pin including a press-fit section press-fitted into said casing,said press-fit section being formed in a taper fashion in such a manneras to gradually decrease its outer diameter towards the end of saidpress-fit section.
 2. The tape cassette as set forth in claim 1, whereinsaid press-fit section is frusto-conical, and its taper is within arange of 1/250 to 1/38.
 3. The tape cassette as set forth in claim 2,wherein said guide pin is formed of non-magnetic stainless steelmaterial by lathe machining.
 4. The tape cassette as set forth in claim1, wherein when said guide pin is used in a manner so as to contact witha tape surface having magnetic substance, the contacting surface of saidtape guide pin having a surface roughness of Rmax 0.1 to 0.4 μm.
 5. Thetape cassette as set forth in claim 4, wherein the contacting surface isfinished by super-finishing after centerless grinding so as toaccomplish a surface-roughness of Rmax 0.1 to 0.4 μm.
 6. The tapecassette as set forth in claim 1, wherein said casing is comprised of anupper half formed of electrical insulating material and a lower halfformed of electrically conductive metal material suitable for thepress-fitting of said guide pin, when a portion of the conductive lowerhalf is exposed outside of a recording and/or reproducing apparatus in astate wherein the tape cassette is set to a predetermined loadedposition, said casing including an insulating member for electricallyinsulating the conductive half, for preventing static electricity frombeing introduced through an exposed portion of the conductive half intothe apparatus, said insulating member comprising the outer wall of saidcasing surrounding the outer perimeter of the conductive half, saidinsulating member overlapping the exposed underside of the conductivehalf by substantially 20 mm.
 7. A tape cassette comprising:a pair ofreels mounted side by side, on which tape is wound; a cassette casingfor rotatably enclosing said pair of reels therein; an upstanding pinbeing press-fitted through the wall of said casing, said pin including acylindrical press-fit section press-fitted into said casing withoutrequirement of a preformed hole; said press-fit section including acylindrical outer peripheral surface coaxial to the axis of the pin, achamfered annular circumference at the lower tip of the cylindricalsurface, terminating in a flat circular end perpendicular to the axisand having an outer diameter less than that of the cylindrical surface,and a chamfered annular circumference joining said cylindrical surfaceand said flat circular end; said chamfered annular circumferenceincluding a predetermined range of geometry and dimension.
 8. The tapecassette as set forth in claim 7, wherein said predetermined range ofgeometry and dimension of said chamfered circumference is a curvedsurface, the curve, in cross-section, corresponding to the perimeter ofa circle with a radius in a range of 0.2 to 0.3 mm, or with a 45°sloped, frusto-conical surface essentially corresponding to thedimension of the curved surface.
 9. The tape cassette as set forth inclaim 8, wherein said upstanding pin is formed of non-magnetic stainlesssteel material by lathe machining.
 10. The tape cassette as set forth inclaim 7, wherein when said upstanding pin is used in a manner so as tocontact with a tape surface having magnetic substance, its contactingsurface having a maximum surface roughness of Rmax 0.1 to 0.4 μm. 11.The tape cassette as set forth in claim 10, wherein the contactingsurface is finished by super-finishing after centerless grinding so asto accomplish a maximum surface-roughness of Rmax 0.1 to 0.4 μm.
 12. Thetape cassette as set forth in claim 7, wherein said casing is comprisedof an upper half formed of electrical insulating material and a lowerhalf formed of electrically conductive metal material suitable for thepress-fitting of said upstanding pin, wherein, when a portion of theconductive lower half is exposed outside of a recording and/orreproducing apparatus in a state wherein the tape cassette is set to apredetermined loaded position, said casing including an insulatingmember for electrically insulating the conductive half, for preventingstatic electricity from being introduced through an exposed portion ofthe conductive half into the apparatus, said insulating membercomprising the outer wall of said casing surrounding the outer perimeterof the conductive half, said insulating member overlapping the exposedunderside of the conductive half by substantially 20 mm.
 13. A tapecassette comprising:a pair of reels mounted side by side, on which tapeis wound; a cassette casing for rotatably enclosing said pair of reelstherein; a driven roller being rotated by a drive device of a recordingand/or reproducing apparatus, associated with said tape cassette, saiddriven roller rotatably supported by an upstanding roller shaft fixed onthe wall of said casing; a pair of idle rollers, each rotatablysupported by an upstanding roller shaft fixed on the wall of saidcasing, wherein each of said roller shafts is press-fitted through thewall of said casing, said roller shafts including a press-fit sectionpress-fitted into said casing, said press-fit section being formed in ataper fashion in such a manner as to gradually decrease its outerdiameter toward the end of said press-fit section; an endless flexibledrive belt for drivingly engaging said driven roller and said idlerollers to rotate said reels, such that a portion of said drive beltbetween said driven roller and each idle roller pressingly contacts aportion of the outermost peripheral surface of the tape wound on eachreel, said drive belt being driven according to rotation of said drivenroller; means for controlling tape tension of the tape during operationof said tape cassette, said means including grease disposed between saidassociated rollers and shafts for lubricating the contacting surfacestherebetween, with a predetermined viscous drag; said grease includingviscosity coefficient of 50 to 500 P (poise) within a grease temperaturerange of -10° to 60° C.
 14. The tape cassette as set forth in claim 13,wherein said casing is comprised of an upper half formed of electricalinsulating material and a lower half formed of electrically conductivemetal material suitable for the press-fitting of said roller shaft, whena portion of the conductive lower half being exposed outside of arecording and/or reproducing apparatus in a state wherein said tapecassette is set to a predetermined loaded position, said casingincluding an insulating member for electrically insulating theconductive half, for preventing static electricity from being introducedthrough an exposed portion of the conductive half into the apparatus,said insulating member comprising the outer wall of said casingsurrounding the outer perimeter of the conductive half, said insulatingmember overlapping the exposed underside of the conductive half bysubstantially 20 mm.
 15. The tape cassette as set forth in claim 13wherein said press-fit section is frusto-conical, and its taper iswithin a range of 1/250 to 1/38.
 16. The tape cassette as set forth inclaim 13, wherein each of said roller shafts is press-fitted through thewall of said casing, said roller shaft including a cylindrical press-fitsection press-fitted into said casing without a preformed hole, thepress-fit section including a cylindrical outer peripheral surfacecoaxial to the axis of said roller shaft, a chamfered annularcircumference at the lower tip of the cylindrical surface, terminatingin a flat circular end perpendicular to the axis and having an outerdiameter less than that of the cylindrical surface, said chamferedannular circumference including a predetermined range of geometry anddimension.
 17. The tape cassette as set forth in claim 16, wherein saidpredetermined range of geometry and dimension of said chamferedcircumference is a curved surface, the curve, in cross-section,corresponding to the perimeter of a circle with a radius in a range of0.2 to 0.3 mm, or with a 45° sloped, frusto-conical surface essentiallycorresponding to the dimension of the curved surface.